Rational Design of Pigment-Polymer Antenna Complexes

Abstract

We report the synthesis of biomimetic programmable pigment-polymer antenna complexes (PPACs) by using reductive amination to bind amine-functional dyes to surface-grafted aldehyde-functional PAGEO5MA chains grown from planar substrates by atom-transfer radical polymerization. The fraction of dye-conjugated repeat units can approach unity under optimized conditions. Dye binding kinetics are strongly influenced by steric factors and can be controlled by varying the polymer grafting density, the dye size and the nucleophilicity of its amine group. Absorption and fluorescence spectra of PPACs produced by conjugating Nile Red ethylamine (NRet) to PAGEO5MA brushes are sensitive to the dielectric environment within the layer. At low dye concentrations, the mean fluorescence lifetime tmean of the chromophore was 1.3 ± 0.1 ns, similar to that obtained for a dilute methanolic solution of NRet (1.17 ± 0.01 ns). tmean decreases with increasing dye conjugation, due to increased dye-dye interactions. However, tmean is higher for NRet conjugated to PAGEO5MA than for NR in a spin-cast film of the dye in poly(methyl methacrylate) at the same concentration, indicating that conjugation to the polymer scaffold minimizes dye aggregation. PPACs offer a potentially versatile route to the production of programmable photonic materials, with efficient conjugation chemistry enabling precise control over dye-dye interactions.